Electrochemical cells to detect and determine the concentration of electrochemically active species (the analyte) in solution by measuring a voltage, a current or the conductance of the solution (hereinafter: "Electrical Properties") between two electrodes are well known in the art. In these solutions, electrochemical measurement is facilitated by charged ions moving relatively freely (i.e. encountering low resistance) in the solution.
Measurements of Electrical Properties is used to monitor many electroactive materials. However, prior art electrochemical cell has been used on-line for only a solution having high conductivity. The prior art electrochemical cell is placed in the solution having high conductivity. With the solution having high conductivity or low resistance, the electrical current or the voltage between electrodes (in a potentiometric measurement) can be measured with relatively low generation of electrical noise interference. Changes in the voltage or current, resulting from changes of the concentration of the analyte at the electrode-solution interface, can be detected. Changes in the conductivity, resulting from changes in the concentration of the analyte in the bulk of the solution, can also be detected. Thus, the signal to noise ratio is high.
For non-conducting or low conducting solutions (hereinafter: "high resistivity liquid"), such as oils, electrochemical cells were ineffective for on-line detection and measurement of analytes dissolved in these solutions. With the solution having high impedance, the amount of electrical noise obscures any reading of changes in the signal (current or voltage).
In order to detect and measure the concentration of analytes in high resistivity liquids, such as oil, a measured amount of the solution is placed in a polar solvent which has increased electrical conductivity to enable effective electrochemical measurements. An electrochemical measurement is made as described above. Thereafter, another measured amount of the solution is placed in the same polar solvent, and a second measurement made. The change in the electrochemical measurement is an indication of change in the concentration of the analyte. See U.S. Pat. Nos. 2,752,566; 3,264,557; 4,313,086; 4,638,305; 4,741,204; and 4,744,870. In U.S. Pat. No. 3,181,058 reference is made to the direct measurement of a test substance wherein an amount of polar solvent is poured into the test substance in order to increase its conductivity. However, there is no disclosure of continuous direct measurement (without sample pre-treatment) of the concentration of analytes in high resistivity liquids.
As can be seen from the foregoing, such a prior art method does not permit the on-line measurement of the concentration(s) of analyte(s) in high resistivity solutions.